The Low Temperature Fischer-Tropsch process for production of wax from synthesis gas using a solid catalyst involves the filtration of wax from a slurry. During normal filtration, the filters are submerged in the slurry and a filter cake of catalyst builds on the filter. The filter cake is normally required for effective filtration. In case of low-level slurry conditions in the filter area of the reactor, the filters together with the filter cake could be exposed to a synthesis gas atmosphere in the head of the reactor. Localised temperature excursions can occur due to the high heat of reaction and low heat removal during conversion of the synthesis gas in a synthesis gas atmosphere. It is an object of the invention to prevent heat excursions which may cause permanent damage to the filters.
In the LTFT reactor the slurry is formed by keeping the solid catalyst in suspension in a hydrocarbon liquid by synthesis gas rising from the bottom of the reactor. Synthesis gas is converted to hydrocarbons. The slurry is a dynamic medium in continuous flux regarding parameters such as, slurry level, density, temperature, catalyst concentration, pressure, gas feed etc. As a result it is a challenge to monitor the slurry level.
One known method of measuring the level of the slurry in the reactor involves the measurement of the density of the slurry, using pressure sensors and transmitters. To measure the level in the reactor using the above density dependence method, is a challenge in environment of continuous formation of products and which is continuously changing density by as much as between 690 kg/m3 to 350 kg/m3.
A second known method of measuring the level of the slurry in the reactor involves using radar reflection of the surface of the slurry. However due to the gas rising through the slurry bed, the dielectric constant of the slurry surface becomes low and the radar beam is largely absorbed by the slurry and results in a weak and unreliable reflected beam.
A third known method uses nuclear sensors and transmitters. The sensor uses a radiation source and detector and is custom designed for the application taking into account the product properties, reactor material and thickness as well as insulation material and thickness.
It is a further object of this invention to provide a reliable method to measure the slurry level in a LTFT reactor.